Microbial growth in commercial water systems can lead to spoilage and surface-fouling. If growth is not adequately controlled, spoilage can lead to offensive odors and reduced function of additives (e.g. microorganisms can produce catalase that hydrogen peroxide uses to enhance brightness and can produce cellulases that can impact fiber strength). If surface-fouling is not adequately controlled, resulting biofilms can interfere with heat-exchange, and in the case of papermaking systems biofilms can create a need to slow down the manufacturing process, shut-down the process to clean these deposits from surfaces, or might slough from surfaces causing holes or spots in the finished paper or board product. Therefore, such waters are treated with biocides to control microbial growth and prevent related problems.
Because spoilage and biofilm-formation contribute to different problems in industrial water systems and planktonic and sessile bacteria respond differently to biocontrol measures, there is a need to monitor the impact of biocontrol programs on these different modes of microbial growth.
Standard techniques typically used to monitor such water systems include standard plate count techniques. These techniques require lengthy incubation periods and do not provide adequate information for pro-active control and prevention of problems related to microbial growth. More recently, adenosine triphoshphate (ATP) measurements have been used as a means of pro-active control. However, the reagents are costly and small volumes are sampled from large water systems. Data collection is also infrequent, leading to significant gaps in data. Therefore, this approach provides limited information on the status of microorganisms in the system of interest. In addition, these approaches are typically used to monitor planktonic bacteria. Although in some cases, surfaces might be swabbed and analyzed in order to quantify biofilm bacteria. These approaches are very tedious and time-consuming.
Dissolved oxygen (DO) probes have been used to measure microbial activity in fluids, as it is well known that microbial activity and aerobic metabolism leads to a decrease in dissolved oxygen concentrations. U.S. Pat. Nos. 5,190,728 and 5,282,537, issued to Robertson et al., disclose a method and apparatus for monitoring fouling in commercial waters utilizing DO measurements. However, the approach requires the use of nutrient additions to differentiate biological from non-biological fouling and there is no mention of how the probe is refreshed for further measurements after the probe surface has fouled. In addition, the approach disclosed requires a means of continuously supplying oxygen.
The standard Clark style electrochemical DO probe has many limitations such as: chemical interferences (H2S, pH, CO2, NH3, SO4, Cl−, Cl2, ClO2, MeOH, EtOH and various ionic species), frequent calibration and membrane replacement, slow response and drifting readings, thermal shock, and high flow requirements across membranes. A new type of dissolved oxygen probe, which has recently been made commercially available by a number of companies (e.g., HACH, Loveland, Colo.), overcomes nearly all of these limitations so that DO can be measured on-line in process waters. This new DO probe (LDO) is based on lifetime fluorescence decay where the presence of oxygen shortens the fluorescence lifetime of an excited fluorophore. The fluorophore is immobilized in a film at the sensor surface and the excitation is provided with a blue LED.
U.S. Pat. Nos. 5,698,412 and 5,856,119, both issued to Lee et al., disclose a method for monitoring and controlling biological activity in fluids in which DO is measured in combination with pH to measure transitions in metabolic behavior, specifically related to nutrient/substrate depletion.
There remains a need for reliable and convenient methods to monitor planktonic and biofilm bacteria in commercial waters, which ensure that biocontrol programs adequately control spoilage and problematic biofilms. These methods should be reagentless to allow measurement of microbial activity in conditions representative of those in the ambient environment (minimal modification). These methods should be automated and should allow for remote control of the monitor, remote access to the data, and remote or automated feed-back control of the biocontrol programs. Ideally, these methods would differentiate microbial activity on surfaces from bulk water activity in order to ensure that biocontrol programs adequately address the increased challenges typically faced when trying to control microorganisms in biofilms. Furthermore, these methods would provide information on the nature of the deposits (biological or non-biological) to ensure that appropriate control measures are applied.